Vehicles equipped with a so-called ATM (Automated Manual Transmission) are known. Such vehicles include motorcycles, ATVs (All Terrain Vehicles) and the like. The ATM performs clutch disengagement and engagement as well as changing of a transmission gear of a transmission by utilizing an actuator, such as a motor.
Japanese Patent Publication 2006-017221 discloses a clutch actuator which generates drive force to perform disengagement and engagement of the clutch and a drive force transmission mechanism which transmits the drive force of the clutch actuator to the clutch. The clutch actuator and the drive force transmission mechanism are arranged outside a casing of a power unit. Specifically, the clutch actuator and the drive force transmission mechanism are arranged behind a cylinder of the power unit above a crankcase. The clutch actuator is attached to the crankcase with a bracket. A drive shaft of the clutch actuator is arranged so as to extend in the vehicle-width direction. The drive force transmission mechanism connects the clutch actuator and a clutch disengaging rod (a push rod) disposed on the outside of the power unit.
However, in the vehicle described in Japanese Patent Publication 2006-017221, the clutch actuator and the drive force transmission mechanism are arranged above the crankcase, resulting in the power unit being upsized in the vertical direction by a space requirement for the clutch actuator and the drive force transmission mechanism.
On the other hand, in order to provide an empty space above the crankcase, an arrangement in which the clutch actuator and the drive force transmission mechanism are placed outside of the side portion of the crankcase may be devised. However, when the clutch actuator and the drive force transmission mechanism are merely arranged at the side portion of the crankcase without a corresponding design modification, the horizontal width (i.e. the dimension in the vehicle-width direction) of the entire power unit (including the clutch actuator and drive force transmission mechanism) becomes relatively large. Consequently, the entire power unit increases in size in the crosswise direction.